1. Field of the Invention
The invention relates generally to image processing. More specifically, the invention relates to enhancement of image characteristics such as contrast, gray level, etc.
2. Description of the Related Art
A digital image such as that captured by a digital camera or scanner can be viewed as consisting of an array of pixel locations each having a particular intensity value. In a Bayer pattern image sensor, each pixel consists of an intensity value associated with one of three color planes, Red, Green or Blue. The image when captured in this form is essentially a gray scale image. Through a process known as color interpolation, the missing two color plane component values for each pixel may be estimated. This process yields a full color image, but may distort or degrade certain image features.
Often in such captured images, it is necessary to highlight or suppress certain image pixels since they were obtained due to poor (low light) or abnormally bright lighting conditions. Such pixels may be xe2x80x9cadjustedxe2x80x9d for their gray scale intensity values. However, such gray scale adjustment cannot be adequately or efficiently performed after color interpolation. In some cases, even after an image is so adjusted and color interpolated, the contrast of the image may be pleasing to human vision. Enhancing the contrast of an image, while perhaps possible after color interpolation, may not properly work after gray scale adjustment. Additionally, if contrast enhancement is first performed before gray scale adjustment, the adjustment may yield poor results. Color shift and loss of color information may result if such techniques are not properly employed.
Thus, there is a need for an integrated gray scale adjustment and contrast enhancement technique that can be applied directly to a captured image.
What is disclosed is a method that specifies identifying a category to which a pixel belongs and performing integrated contrast enhancement and gray scale adjustment on the pixel in accordance with the identified category of the pixel.